Contaminant removal effectiveness

The contaminant removal effectiveness can be used when emission data for contaminant sources are available. 

Air exchange efficiency indices can be used for cases where no or little information on sources is available, whereas ventilation efficiency, which concerns workers, can be used where very detailed information is available on sources and activities. 

As mentioned above, the traditional definition of ventilation efficiency or, in approved terms, contaminant removal effectiveness, is the ratio between contaminant concentration in the exhaust air and the concentration at a point in the occupied space, i.e., 

In other words, this contaminant removal effectiveness is a measure of how much cleaner the air is in the occupied spaces than in the exhaust. See Fig. 8.8. 

When detailed information on heat and contaminant sources is available, assessment of design is improved by evaluating the effectiveness of contaminant removal achieved by space ventilation. The set of contaminant removal effectiveness indices in Table 8.5 is given in accordance with contemporary use of indices. 

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Ventilation efficiency has traditionally been defined as the ratio between contaminant concentration in the occupied spaces and the concentration in the exhaust air. Sandberg and Skaret differentiate between the terms air change efficiency and contaminant removal effectiveness. Air change efficiency is a measure of how effectively the air present in a room is replaced by fresh air from the ventilation system, whereas contaminant removal effectiveness is a measure of how quickly an air-borne contaminant is removed from the room. A third similar criterion that is used is contaminant removal efficiency. ... 

Application of contaminant removal effectiveness indices is relatively simple for scenarios with one or a few dominant contaminants being released. That is often the case in industrial mails. Where there are many polluting substances to consider the contaminant removal efficiency should ideally be evaluated for each one. Consequently, applications for regular indoor climate— for example, in a restaurant—are limited, except when addressing specific pollutants like smoking and ctxrking hunes. 

There are four principal ideas in achieving uniform conditions m the control led zone and a high hear and contaminant removal effectiveness ... 

The effect of the plume airflow rate and the turbulent mixing airflow rate through the zone boundary is presented in Fig. 8.35. The heat removal effectiveness and contaminant removal effectiveness are presented as functions of the relative airllow rate. 

The effect of the local exhaust airflow rate in the lower zone is presented in h ig, 8.37. The heat removal effectiveness e and contaminant removal effectiveness Cf (determined by extract air) are presented as functions of the local exhaust airflow rare. The total heat load is 60 W m - and the power of one heat source is 500 W. The supply airflow rate is 8 L s m . ... 

A U.S. EPA study (41) showed that soil vapor extraction (SVE) is an effective treatment for removing volatile contaminants from the vadose zone. Sandy soils are more effectively treated than clay or soils with higher organic content because higher air flows are possible in sand and clays—organic soils tend to adsorb or retain more contaminants. Removal of volatiles is rapid in the initial phase of treatment and thereafter decreases rapidly thereafter-an important consideration in the design of air emissions control over the life of the project. 

Color can be removed effectively and economically with either alum or ferric sulfate at pH values of 5—6 and 3—4, respectively. The reaction is stoichiometric and is a specific reaction of the coagulant with the color to form an insoluble compound (17). The dosage required may be as high as 100—150 mg/L (380—570 mg/gal). Raw-water colors may be as high as 450—500 units on the APHA color scale. The secondary MCL (maximum contaminant level) for color in the finished water is 15 units, although most municipal treatment plants produce water that seldom exceeds 5 units. 

Foaming is usually caused by contamination of glycol with salt, hydrocarbons, dust, mud, and corrosion inhibitors. Remove the source of contamination with effective gas cleaning ahead of the absorber, improved solids filtration, and carbon purification. 

The contaminant removal efficiency can be derived from the coniaminaiu removal effectiveness as follows ... 

A similar temperature and contaminant distribution throughout the room is reached with stratification as with a piston. The driving forces of the two strategies are, however, completely different and the distribution of parameters is in practice different. Typical schemes for the vertical distribution of temperature and contaminants are presented in Fig. 8.11. While in the piston strateg) the uniform flow pattern is created by the supply air, in stratification it is caused only by the density differences inside the room, i.e., the room airflows are controlled by the buoyancy forces. As a result, the contaminant removal and temperature effectiveness are more modest than with the piston air conditioning strategy. 

Advantages include low concentration in the ventilated zone can be achieved and relatively high contaminant removal and temperature effectiveness. However, the srratificacion strategy is sensitive to disturbances and stagnant areas with high... 

The zoning method offers better contaminant removal and thermal effectiveness than with mixing, limited control of the flow patterns in the ventilated zone, and the ability to avoid stagnant areas with high local concentrations in the ventilated zone. However, partial mixing of contaminants in the ventilated zone decreases its effectiveness. 

The contaminant removal and temperature effectiveness in the mixing strategy are equal to 1. In practical installations incomplete mixing in the room and unfavorable temperature gradient and location of the exhaust openings in relation to air supply may, however, cause short-circuiting of the supply air into the exhaust openings and the efficiency may remain below 1. 

Substantial quantities of aluminum, copper, and steel are reused as scrap. The challenge is to purify the scrap metal sufficiently to process it for reuse. There is opportunity for new processes that can remove unwanted elements—either alloyed or piece contaminants—more effectively and at lower cost than current processes. 

We recently demonstrated that photocatalyzed destruction rates of low quantum efficiency contaminant compoimds in air can be promoted substantially by addition of a high quantum efficiency contaminant, trichloroethylene (TCE), in a single pass fixed bed illuminated catalyst, using a residence time of several milliseconds [1-3]. Perchloroethylene (PCE) and trichloropropene (TCP) were also shown to promote contaminant conversion [2]. These results establish a novel potential process approach to cost-effective photocatalytic air treatment for contaminant removal. 

For some applications, an adsorbent may be impregnated with a material that enhances its contaminant-removal ability. The improved effectiveness may be related to any of several mechanisms. The impregnating material may react with the vapor contaminant to form a compound or complex that remains on the adsorbent surface. Some impregnants react with the contaminant, or catalyze reactions of the contaminant with other gas constituents, to form less noxious vapor-phase substances. In some instances, the impregnant acts as a catalyst intermittently, for example, under regeneration conditions. In this case, the contaminant is adsorbed by physical adsorption and destroyed by a catalytic reaction during regeneration. 

Chapter 4 described methods for limiting the time of exposure to weapons of mass destruction that utilize no explosives (e.g., aerosol delivery) or use of conventional explosives (e.g., dirty bomb). The basic procedure is to leave the contaminated area as quickly as possible, enter a nearby building to shelter against airborne contamination, remove soiled articles of clothing, and wash all exposed body parts (including the mouth and hair) as soon as possible. In Chapter 4, the time factor is applied primarily to limit the chances of potential future health effects. In this section, the time factor is applied after a nuclear explosion to prevent serious bodily harm and death. 

From an isotherm test it can be determined whether a particular organic material can be removed effectively. It will also show the approximate capacity of the carbon for the application and provide a rough estimate of the carbon dosage required. Isotherm tests also afford a convenient means of studying the effects of pH and temperature on adsorption. Isotherms put a large amount of data into concise form for ready evaluation and interpretation. Isotherms obtained under identical conditions using the same contaminated groundwater for two or more carbons can be quickly and conveniently compared to determine the relative merits of the carbons. 

Because of the complex composition of most groundwaters, no one unit operation is capable of removing all of the contaminants present. It may be necessary to combine several unit operations into one treatment process to remove effectively the contaminants required. To simplify and make visible the selection of the applicable treatment trains, a number of unit operations and the waste types for which they are effective are presented in Table 8.1. 

Electrochemical technique (also electrocoagulation) is a simple and efficient method for the treatment of potable water. This process is characterized by a fast rate of contaminant removal, a compact size of the equipment, simplicity in operation and low capital and operating costs. Moreover, it is particularly more effective in treating wastewaters containing small and light suspended particles, such as oily restaurant wastewater, because of the accompanying electroflotation effect. 

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